The invention concerns an apparatus for and a method of pneumatically conveying powder substancesxe2x80x94possibly with the use of at least one filterxe2x80x94in a pipe system, wherein the substance is sucked in with a reduced pressure and a given volume is discharged with an increased pressure to be passed further along. The invention also concerns the use of that apparatus and/or that method.
An apparatus and a method of that kind are known from WO 98 17 558 to the present inventor. EP-A-0 574 596 also describes an installation for pneumatically transloading cement from ships into silos by means of a so-called lock-type container comprising a plurality of container segments; disposed in the uppermost container segment is an exhaust air filter while the lowermost container segment tapers in a funnel-like configuration.
In consideration of those factors the inventor set himself the aim of increasing the degree of accuracy of continuous metering in inexpensive conveyance of powder substances.
That object is attained by the teaching set forth in the independent claims; the appendant claims set forth advantageous developments. The scope of the invention also embraces all combinations of at least two of the features disclosed in the description, the drawing and/or the claims.
In accordance with the invention, within the pipe system, the apparatus has at least one metering chamber which can be filled and emptied alternately by way of a control unit. In addition it has proven to be advantageous to connect to the metering chamber on the one hand a gas pressure conduit and a suction conduit and on the other hand a feed conduit and a discharge conduit; the gas pressure conduit and the suction conduit are preferably connected with the interposition of a filter in order to prevent the ingress of substances being conveyed.
In accordance with a further feature of the invention the metering chamber is of a diameter of between 0.5 and 100 mm, preferably between 1 and 80 mm, while the length thereof is between 5 and 30 times, advantageously between 10 and 20 times, the diameter.
In addition at least one control unit is to be associated with the conduits of the pipe system; at least in the region of the control unit the conduits are to be of a variable cross-section and in particular are to be elastically deformable.
By way of example the control unit may be provided with two linear abutment regions which extend at a spacing relative to each other and with which are associated conduits which are deformable in cross-section and which can be applied alternately. Desirably, for that purpose, abutment regions are in the form of sides of a control frame.
The invention also provides that at least one pressure-generating elementxe2x80x94for example a control pistonxe2x80x94is movably mounted in the control frame and near the abutment regions or frame sides is provided with clamping bars or the like pressure members which, to deform the conduit cross-sections, are moved against same.
In another embodiment the control unit has an abutment region for pressure-generating elementsxe2x80x94in particular control pistonsxe2x80x94, with each of which is associated a pair of conduits.
The invention also provides a cam disk or cam shaft whose cam, during the rotation thereof, actuates metering valves which project into the path of movement.
In accordance with the invention, a continuous metering action of substantially higher accuracy is achieved as it is implemented by means of a plurality of small and accurately matched partial metering steps. The apparatus in accordance with the invention not only permits metering of a given amount but also affords the possibility of feeding a given amount of a product in powder form to a consumer, in a constant unit in respect of time. In order to be able to carry out such a metering procedure which is a pulsed procedure or which comprises a plurality of quantums, an accurately operating control system is of particular significance.
The method according to the invention is distinguished in that at least one metering chamber which is disposed within the pipe system 111 is alternately filled and emptied by way of a control unit. In addition the control action is to be effected by closing the suction conduit and the gas pressure conduit, in particular by clamping off feed hoses for vacuum and increased pressure.
A reduced pressure of between 10 and 600 mbarxe2x80x94preferably between 20 and 500 mbarxe2x80x94has proven to be advantageous, and an increased pressure of between 01 and 6 bars, preferably between 02 and 5 bars, has proven to be advantageous.
In accordance with the invention, with the control pulse for a piston of the control unit, all the deformable feed and discharge conduits which are to be controlled are closed in very short control pulse times; advantageously, control pulses for sucking in and ejecting the powder product are of a frequency of between 0.1 and 5 seconds, preferably between 0.2 and 4 seconds.
To protect the metering zone, the powder material may also be conveyed under protective gas.
All in all there is here an invention which can attain in a brilliant manner the object seen by the inventor, in particular for conveying powder materials, including metal substances of that kind.